The present invention relates to a method for heating the paving screed of a road finisher having a heating means within the paving screed including several electric heating elements supplied by a rotary current generator with current and to an electric heating means of a paving screed of a road finisher having a plurality of heating elements associated within the paving screed to working components. The heating elements are connected by a control device each alone or several in groups to a rotary current generator.
It is known from practice to heat operation components of the paving screed of road finishers either electrically or by gas. The heating particularly is carried out at the so-called tamper-bar, the smoothing sole plates and at occasionally provided pressing bars. Said operation components have to be heated so that the heat paving material processed by them does not stick thereon. The temperature of the paving material as processed by the paving screed amounts to e.g. 170xc2x0 C. Heating must be continued during paving. For example, in an electric heating means of a paving screed electric heating rods are distributed in said paving screed and are supplied by rotating current of a rotating current generator driven by the primary drive source, mostly a diesel engine. It is usual practice to operate the heating means of the paving screed permanently and under full power. However, this is loading the rotary current generator extremely, particularly in case of tough operating conditions and/or means a considerable waste of energy. It is an object of the invention to provide a method as men toned above and a paving screed heating means allowing to carry out said method, by which energy can be saved and long service times of the rotary current generator can be achieved.
Said object can be achieved by the features of claim 1 and the features of independent claim 9.
In case of the danger of an overload or overheating of the rotary current generator due to tough operation conditions, the load of the rotary current generator is reduced by switching on and off at least one heating element or switching over between at least two heating elements in a timed fashion or in cycles, respectively, so that the rotary current generator may cool down or does not reach its critical operation temperature, respectively. In this case the finding is considered that the already heated operation components of the paving screed have remarkable heat storing properties and a long heated after run time despite switching off of their heating elements during which after run time no significant temperature reduction occurs, and that additionally during the paving phase the heated paving material is contributing sufficient heat on its own so that said cycles of switching on/off or switching over do not result in a paving quality reduction or in undesired contaminations of the operation components. Alternatively or additively, the contributed heat of the processed paving material allows to save energy with the help of said cycles. Nevertheless, a sufficient heating of the screed is assured. Expediently, said cycles are carried out exclusively during the paving operation of the paving screed, in order to not delay heating-up the paving screed, and to use the heat contained in the paving material in a beneficial way when the road finisher is travelling with paving speed and when sufficient assisting heat is available.
The management-section of the heating means optionally monitor different operational parameters at the side of current generation and within the road finisher in order to adjust the consumed power towards a tolerable maximum. This is done by modulated switching on and switching off of heating elements. By said method heat contained in the paving material is used in an advantageous fashion, energy is saved, and the rotary current generator is prevented from excessive load, e.g. in case of tough operating conditions.
For the safety of the rotary current generator the timed control in cycles in any case can be carried out when the operation temperature of the rotary current generator has exceeded the ideal operation temperature by a predetermined temperature value, e.g. 20xc2x0 C. Said condition normally is sufficiently far below the critical temperature threshold of the rotary current generator. By means of timed changeover switching steps the load of the rotary current generator can be reduced to an extent that the generator again cools down to its ideal operation temperature.
Expediently the heating elements of the left and the right paving screed half are alternatingly switched on and off. This means, of course, that even extension screed parts at the left and right base screed halves will be incorporated into said measure and, occasionally even mounted boardening parts which also need to be heated. For the time period of the timed switching cycles the rotary current generator needs to produce only about 50% of the maximum power.
Expediently the duration of the cycles amount to about 30 seconds. Those are time periods showing no significant influence on the paving quality or the tendency of the paving screed to become contaminated and which assure that no significantly tangible temperature variations occur in the paving screed.
To start with the timed switching cycles also e.g. the following monitored operational parameters are decisive: xe2x80x9cis road finisher travelling, is paving material conveyed, and is rated speed of the primary drive source reachedxe2x80x9d.
The operational temperature of the rotary current generator can reliably be detected by temperature sensitive resistors. A plurality of such temperature sensitive resistors is expedient in order to allow to survey different temperature threshold values.
A significant relief of the rotary current generator already can be achieved if the heating elements of one screed half are switched off while the heating elements of the other screed half are switched on. Said rotary current generator even could be relieved further if there are delay time periods adjusted between said switch over steps. Alternatively, it is possible to switch over with a timewise overlapping. The delay times or said timewise overlappings can be adjusted in proportion to the initial temperature of the generator.
Temperature sensitive resistors placed in the coiling of the rotary current generator reliably detect actual temperature values there.
In case that there is an additional heating system extending across the entire screed, said additional heating system expediently is excluded from the timed switching cycles.
Shockproof and/or CEE-outlets provided at the road finisher and/or at the paving screed allow to connect additional assistant systems, e.g. illumination systems for maintenance and/or night operation. Said outlets are controlled by said section via relays or contactors.
The actual current value is measured by means of a current converter. On the basis of said current value the power is calculated. The power information is transmitted to the section.
In order to actually only control in cycles when this is useful, the heating selecting switch can suppress the control operation in cycles in the xe2x80x9cmanualxe2x80x9d position of the heating selector switch.
Expediently further outlets are provided at the paving screed serving to connect heating elements of broadening parts of the paving screed. Said heating elements of the broadening parts thus take part in the timed switching cycles.